Industrial workers must be able to function in environments where chemical hazards are present. Thus, they need protection against hazardous chemicals used in the workplace. Particularly relevant is the use of respiratory protection for environments where workers are exposed to chemical vapors/gases. In most cases, respiratory protection consists of a respirator face mask that is equipped with replaceable filter beds known as cartridges. For these types of respirator masks, once a cartridge's capacity for adsorbing chemicals is used up, the expired cartridge can simply be thrown away and replaced with a fresh, unused cartridge. Unfortunately, there is no reliable way to determine when the filter cartridge has expired, thus the wearer is often exposed to the vapors after the cartridge is saturated, but before it is replaced. An OSHA standard for respirator cartridge use requires that employers provide either a rigorous change-out schedule or use a National Institute of Occupational Safety and Health (NIOSH)-certified end-of-service-life indicator (ESLI) to determine when a respirator cartridge needs to be replaced. Because no reliable, certified commercially available ESLI has been developed, employers rely on respirator change-out schedules. These schedules, however, are often inaccurate and unreliable because the input parameters used to calculate the lifetime of the cartridges are rarely accurately known. As a result, wearers of the mask often do not follow the change-out schedules and are frequently exposed to chemical vapors prior to changing respirator cartridges. Further, the Bureau of Labor Statistics and NIOSH surveys show that some 20- 30% of all the workers determine their own respirator change-out schedules, which is against OSHA regulations. An effective, NIOSH-approved ESLI technology that warns the user of impending contaminant breakthrough would provide an unambiguous means of safely determining when a respirator cartridge should be replaced. To date, however, there is no commercial ESLI technology for respirator cartridges that responds to the types of contaminants that are prevalent in common industrial environments. Should this technology be available in respirator cartridges, not only would an ESLI prevent the harm to workers that is caused by incidental overexposure to vapors, but it would be attractive to employers because it would eliminate the added expenses incurred from unnecessary replacement of partially used cartridges resulting from conservative change-out schedules. In summary, an effective ESLI technology would improve the safety of the more than 12 million annual respirator cartridge users in the U.S., and it would be adopted because it saved money (an effective but expensive system would do little to improve safety because few companies would use it). In the Phase I project, TDA has developed and demonstrated a colorimetric ESLI that changes color in response to organic vapors, acid gases and basic gases. In the Phase II proposal, TDA proposes to further develop the end of service life indicator (ESLI) and incorporate it into prototype respirator cartridges with the help of our collaborators.